Approximately 70 million CT studies are performed each year in the U.S., which accounts for about 50% of the radiation dose exposure administered in the healthcare setting. In large part due to CT scans, the average lifetime diagnostic radiation dose received by patients is up sevenfold from 1980. Numerous studies and reports have been published recently concerning potential dangers of low-dose radiation exposure (similar to the dose levels from 2-3 CT studies). A standard CT scan of the abdomen/pelvis is equivalent to approximately 150-200 chest X-rays. Thus, for a patient who has had a CT scan and a number of X-rays, the larger contribution to the radiation dose exposure likely results from the CT scan (although there are other procedures such as the PET-CT, and long interventional procedures using fluoroscopy, which also contribute to significant radiation exposures). Pediatric patients are at higher risks compared to adults for a given radiation dose.
Adverse events involving inadvertent healthcare-related radiation overexposure involving CT have caused much public concern about the safety of CT scans. In one instance, a hospital gave 8× the normal dose for head CT studies involving more than 250 patients. In another instance, a two-year old pediatric patient had the same region of his head scanned over 150 times, lasting over an hour during the CT exam. These radiation overexposure events can occur because of policy errors (e.g., flawed CT protocols), human errors, or machine errors. Physicians can attempt to minimize the possibility of these risks, and correct the errors before they cause detrimental effects to patients, but only to the extent that these radiation overexposure events can be detected.
Some of the overexposures were only detected as a result of patient symptoms (e.g., erythema, hair loss, etc), or observations by the patients or their family members. Recent campaigns promoting radiation safety and awareness such as “Image Gently,” and the color coding of pediatric low-dose protocols by vendors to increase compliance, have improved awareness for both the public and medical professionals. However, these efforts may not be sufficient.
In addition to diagnostic CT, use of CT for screening studies has also dramatically increased, particularly for lung and colon cancers. There have been concerns about the risk of radiation exposure from CT colonography.
The increase in CT usage partly results from demand increase from both referring clinicians and patients themselves. Improvements in CT scanners in image quality and functionality make these studies easier to perform, and this may also increase the tendency of more CT studies.
While there are no studies yet directly connecting CT radiation to cancer-related deaths, some recent studies have attempted to extrapolate the risk of CT-associated cancers to the data from the Hiroshima atomic bomb survivors. One particular atomic bomb survivor cohort of 25,000 people received an average dose of 40 millisieverts (mSV) (roughly the equivalent of 2-3 CT studies) demonstrated a significant increase in overall cancer risk and mortality. One commonly cited publication estimates that up to 1.5-2% of all current cancers in the U.S. may be attributed to CT studies, and therefore despite of a small individual risk, the population risk to CT use may be significant.